恶性疟原虫乳酸脱氢酶基因克隆、可溶性表达及突变体活性分析

Cloning,Soluble Expression and Mutant Activity Analysis of Lactate Dehydrogenase Gene from Plasmodium falciparum

为了建立以代谢酶类为靶点的新型抑制剂乃至抗疟药高通量筛选和体外评价平台,从恶性疟原虫海南株FCC1中扩增出乳酸脱氢酶基因(PfLDH)。利用融合表达载体pGEX-2TK和pET-29a(+)将PfLDH基因导入大肠杆菌BL21和BL21(DE3)中高效表达,结果成功地在菌体裂解上清液中检测到高酶促活性的PfLDH。以pGEX-2TK为载体的PfLDH基因主要以包涵体形式表达,以pET-29a(+)为载体的PfLDH基因则能大量表达可溶性PfLDH,表明后者更适合用来大量制备重组PfLDH。同时,根据SDS-PAGE图谱并结合序列分析结果,对基因扩增中随机产生的PfLDH截短序列进行了筛选和克隆,从中获得4个携带终止突变并分别编码45、80、149和263个氨基酸残基的“提早成熟”基因PfLDH-Δ271、-Δ236、-Δ167和-Δ53。通过基因表达及酶促活性测定,评价了提前终止突变对PfLDH活力的影响,为探讨PfLDH结构与功能的关系提供了依据。

To establish a platform for high throughput screening and in vitro evaluating novel metabolic enzyme-targeted inhibitors towards anti-malarial drugs, a lactate dehydrogenase gene of Plasmodium falciparum （PfLDH） was amplified from the Hainan isolate FCC1/HN. The fusion expression vectors, pGEX-2TK and pET-29a（ ＋ ）, were utilized to introduce the PfLDH gene into strains of Escherichia coli, BL21 and BL21 （DE3）, for over-expression. Consequently, the enzymatic activity of PfLDH was successfully detected in the suspension of lytic bacteria. The PfLDH gene cloned in pGEX-2TK was mainly expressed as inclusion bodies, while the same gene cloned in pET-29a（ ＋ ） was nearly expressed in a soluble form of PfLDH, demonstrating the latter vehicle might be more suitable for the large-scale preparation of recombinant PfLDH. Furthermore, according to the electrophoregram of SDS-PAGE and the sequencing data, a series of truncated PfLDH sequences generated randomly from gene amplification were screened and cloned, from which four pre-matured genes with a terminator mutation, PfLDH-△271 ,-△236, -△167 and -△53 coding for 45,80,149 and 263 amino acid residues, were individually recovered. Through the gene expression and enzymatic activity measurement, the effect of pre-matured terminator mutation on the activity of PfLDH was evaluated, which should pave the way for probing the relationship between structure and function of PfLDH.